Welcome to FDMB!
Let me suggest that you add to your subject line so it reads, "15 year old Tom in England." You'll get more specific information if people know where you live. Most of the membership here is from the US or Canada so we often make incorrect assumption.
One of the more popular low carbohydrate treats are freeze dries proteins. For example, freeze dried chicken where chicken is the only ingredient in the treat. There are also cats who will happily gobble down cooked or even raw chicken.
The amount of insulin necessary to treat your cat's diabetes is irrelevant. Your cat needs what he needs to get his numbers in a normal range (2.8 - 6.7 mmol/L or 50 - 120 mg/dL if in the US). The dosing methods we use involve dose changes in 0.25u amounts. We have a lot of good information on using Prozinc in our
Prozinc Insulin Support Group.
It would help us enormously if you set up your signature so we don't plague you with the same questions all the time and set up a spreadsheet. The instructions are in
this link along with some other very helpful information. I'm also tagging one of our members,
@Bandit's Mom if you need some help getting the spreadsheet set up. The spreadsheet allows you to keep all of your test data in one place and it allows us to view Charlie's progress and offer any assistance should you need it.
You might also find this
food chart helpful. We encourage caregivers to feed their cat a low carbohydrate (under 10% carb) diet. Most people feed their cats around 5%. The list I linked is for foods that are available in the UK. You'll also want to keep some medium (10 - 15%) and high (over 15%) carb food on hand.
Please let us know if you have questions. The members here are very generous with their knowledge and time.